I have a MegaMat 10 single and Duo; many years of direct experience. When it was just me soloing in my Small XL Columbus the single worked great. Yes, going from sea level to 10,000' or visa-versa is met with either adding or subtracting air (per LCPhil: Leave the valve open to auto compensate); but wasn't a deal breaker for me.
The Duo however, even though "we" used it more than a few times in the Columbus, is about 2" too wide to be considered a good fit; its doable but not ideal. Medium width Columbus wouldn't be a problem. But, and I'll save the chatter, even though I'm sleeping on my Duo in the house for the time being, like any air mattress with two or more people trying to sleep on it, it's just not the right tool for the job (a challenge to get the most comfy air pressure for two disproportionate weight people as well as bouncy when one person rolls/shifts or gets up).
But, negative performance nits for two people aside, they are the most comfortable air based mattresses/pads I've ever slept on.